Coulomb Explosion Imaging of Complex Molecules Using Highly Charged Ions

Rapidly stripping off multiple electrons from the target and triggering complete fragmentation with each constituent atom being charged up are ideal prerequisites for Coulomb explosion imaging. Here, we demonstrate that highly charged ion beam with energy in the Bragg peak region is a powerful tool capable of meeting these requirements. Using the $112.5\text{ }\text{ }\mathrm{keV}/\mathrm{u}$ ${\mathrm{C}}^{5+}$ beam, we successfully imaged the structures of pyridazine, pyrimidine, and pyrazine, three isomers of ${\mathrm{C}}_{4}{\mathrm{H}}_{4}{\mathrm{N}}_{2}$, by detecting ionic fragments ${\mathrm{H}}^{+}$, ${\mathrm{C}}^{2+}$, ${\mathrm{C}}^{+}$, and ${\mathrm{N}}^{+}$ in quadruple coincidence. The three isomers are unambiguously distinguished in the spectra of angular correlation between different fragments, and their structures are clearly visualized in momentum images. More importantly, taking the advantage of fast colliding interaction that creates high charge states on a subfemtosecond timescale, our approach effectively suppresses the distortion of molecular configuration during explosion, ensuring the high accuracy in structural imaging. This is confirmed by the quantitative agreement of momentum magnitudes between the point-charge model and the experiment for all fragments including hydrogen. Our work demonstrates that highly charged ion induced Coulomb explosion is a powerful tool for precisely imaging the initial structures of complex molecules.